This invention relates to microstrip antennas and more particularly to a technique for feeding microstrip antennas to obtain wider bandwidths than obtained in prior single element microstrip antennas.
For most applications using thin microstrip antennas, it is very difficult to produce antennas that have very wide bandwidth. Microstrip antennas by nature are limited in bandwidth to approximately 1% to 5% depending on the thickness of dielectric separating the ground plane from the element Previously, the use of thicker and larger antennas that protrude above the aircraft skin was necessary in order to obtain wide band performance. Another approach was to use a plurality of microstrip antenna elements stagger tuned to provide the bandwidth desired; however, such approach is sometime undesirable since it also produces complex radiation patterns.
The present invention uses a technique that provides bandwidth improvement to approximately 30%. The feeding technique of the present invention can be used with any of a variety of microstrip antennas, such as disclosed in: U.S. Pat. No. 3,972,049 for Asymmetrically Fed Electric Microstrip Dipole Antenna; U.S. Pat. No. 3,978,488 for Offset Fed Electric Microstrip Dipole Antenna; U.S. Pat. No. 3,984,834 for Diagonally Fed Electric Microstrip Dipole Antenna; U.S. Pat. No. 4,370,657 for Electrically End Coupled Parasitic Microstrip Antennas; as well as other adaptable microstrip antennas. By using the techniques of this invention, a less expensive microstrip antenna can be made to meet broadband requirements that more expensive or more complex microstrip antennas cannot meet. This invention can extend the VSWR bandwidth of an existing microstrip antenna system by more than a factor of four.